1. Field of the Invention
The present invention relates generally to a magnetic tape cassette, particularly to a magnetic tape cassette comprising a tape reel having upper and lower flanges and a magnetic tape cassette casing formed of upper and lower housings. More particularly, the invention relates to a structure for preventing dust from being produced by friction between the flanges and the housings.
2. Description of the Prior Art
Magnetic tape cassettes including two magnetic tape reels and a magnetic tape casing are common.
Conventionally, in such magnetic tape cassettes, the tape reel assembly consists of a cylindrical drum section having upper and lower reel flanges integrally attached onto upper and lower faces thereof, respectively, and the casing consists of upper and lower housings. The lower flange has a cylindrical hub section projecting from the outer surface thereof and comprises a substantially cylindrical recess for receiving a reel shaft of a recording and/or reproducing apparatus. The tape reel is rotatably received within a circular opening formed in the lower housing through the cylindrical hub section. A clearance between the outer peripheral surface of the cylindrical hub section and the inner peripheral surface of the circular opening is standard among tape cassette manufacturers. Since the alignment of the reel shaft may vary slightly between cassette players, the clearance is necessary in order to assure the smooth rotation of the tape reel assembly without friction between the hub section and the circular opening formed in the cassette case for receiving it. The clearance is referred to as a "G spec.".
However, in such a magnetic tape cassette, the bosses of the tape reels are often caused, due to vibration or shocks, to come out of the respective openings of the lower housing and, as a result, dust is produced by the friction between the edges of the upper and lower flanges and inner walls of the housing.
Thus, in conventional tape cassettes, the degree of play of the tape reel perpendicular to the center axis thereof is either defined by the clearance between the edges of the upper and lower flanges of the tape reel and the inner surfaces of side wall of the housing, or defined by the clearance between the inner periphery of the circular opening and the corresponding hub section of the reel assembly.
Recently, magnetic tape cassettes with provisions for preventing the bosses of the tape reels from coming out of the respective openings of the lower housing have been proposed.
One such magnetic tape cassette has been disclosed in the Japanese Utility Model First Publication (Jikkai) Showa No. 61-140491. This magnetic tape cassette includes an inwardly extending annular projection in the periphery of the circular opening of its lower housing, for preventing the bosses of the tape reel assemblies from coming out of the respective openings in the lower housing, and for preventing fracturing of the upper flange. In such magnetic tape cassettes, there is a problem in that, since the reels are supported and guided near the central axes thereof, they can easily become inclined, with the result that the bosses come out of the hole in the lower half of the casing and the reel becomes free to slide around the inside of the cassette casing. Another result of the inclination is that the flanges impinge at their outer edges upon the upper and/or lower inner surfaces of the casing, with the result that they may become cracked near the hubs.